CBSE Class 7 Science Physics Chemistry Biology Worksheet Set 03

PHYSICS

Question 1. Amit has an iron piece of mass 79g. He measured the volume of the iron piece by placing it in a measuring jar. Observe the given pictures. Calculate (i) the volume of the iron piece and (ii) the density of iron
Answer: Initial water level without iron piece (from first measuring jar) = \(30\text{ cm}^3\)
Final water level with iron piece (from second measuring jar) = \(40\text{ cm}^3\)
(i) Volume of the iron piece = Final volume - Initial volume = \(40\text{ cm}^3 - 30\text{ cm}^3 = 10\text{ cm}^3\)
Mass of the iron piece = \(79\text{ g}\)
(ii) Density = \(\frac{\text{Mass}}{\text{Volume}}\)
Density of iron = \(\frac{79\text{ g}}{10\text{ cm}^3} = 7.9\text{ g/cm}^3\)
In simple words: The volume is found by checking how much the water level rises when the iron is dropped in, and the density is mass divided by that volume.

Exam Tip: Always subtract the initial reading from the final reading of the measuring cylinder to get the volume of an irregularly shaped solid.

Question 2. Calculate the density of a steel piece of volume \(12\text{ cm}^3\) and mass \(96\text{ g}\).
Answer: Mass = \(96\text{ g}\)
Volume = \(12\text{ cm}^3\)
Density = \(\frac{\text{Mass}}{\text{Volume}}\)
Density = \(\frac{96}{12} = 8\text{ g/cm}^3\)
In simple words: Divide the mass of the steel by its volume to get its density.

Exam Tip: Include proper units in your final answer (\(\text{g/cm}^3\)).

Question 3. What is the mass of \(5\text{ m}^3\) of cement of density \(3000\text{ kg/m}^3\)?
Answer: Volume = \(5\text{ m}^3\)
Density = \(3000\text{ kg/m}^3\)
Mass = Density \(\times\) Volume
Mass = \(3000\text{ kg/m}^3 \times 5\text{ m}^3 = 15000\text{ kg}\)
In simple words: Multiply density by volume to find the total mass.

Exam Tip: Rearrange the density formula (\(\text{Density} = \frac{\text{Mass}}{\text{Volume}}\)) to \(\text{Mass} = \text{Density} \times \text{Volume}\) when solving for mass.

Question 4. ANSWER IN ONE WORD
a) The amount of matter contained in a body-
Answer: Mass
In simple words: Mass is the quantity of matter in an object.

Exam Tip: Do not confuse mass with weight; mass remains constant everywhere.

Question 4. b) The apparatus used in the Physics lab to measure the weight of an object-
Answer: Spring balance
In simple words: A spring balance measures force or weight.

Exam Tip: Beam balance measures mass, whereas a spring balance measures weight.

Question 4. c) The mass per unit volume of an object-
Answer: Density
In simple words: Density tells how compact a substance is.

Question 4. d) S.I. unit of density-
Answer: Kilogram per cubic metre (\(\text{kg/m}^3\))
In simple words: It is the standard international unit for density.

Exam Tip: CGS unit is \(\text{g/cm}^3\), but SI unit is \(\text{kg/m}^3\).

CHEMISTRY

Question 1. Write the formulae of the following compounds:
a) Sulphuric acid
Answer: \(\text{H}_2\text{SO}_4\)
In simple words: Sulphuric acid consists of two hydrogen atoms, one sulphur atom, and four oxygen atoms.

Exam Tip: Commonly known as the king of chemicals.

Question 1. b) Sodium bicarbonate
Answer: \(\text{NaHCO}_3\)
In simple words: Also known as baking soda.

Exam Tip: Be careful with prefixes and valencies when writing chemical formulas.

Question 1. c) Silver nitrate
Answer: \(\text{AgNO}_3\)
In simple words: Silver combined with the nitrate radical.

Exam Tip: Silver has a valency of +1 and nitrate has a valency of -1.

Question 1. d) Calcium carbonate
Answer: \(\text{CaCO}_3\)
In simple words: The primary component of limestone, chalk, and marble.

Exam Tip: Calcium has a valency of +2 and carbonate has a valency of -2.

Question 2. From the given formulae, write down the names of the chemical compounds:
a) \(\text{CH}_4\)
Answer: Methane
In simple words: The simplest alkane and main component of natural gas.

Exam Tip: Also known as marsh gas.

Question 2. b) \(\text{H}_2\text{O}\)
Answer: Water
In simple words: Essential universal solvent for life.

Exam Tip: Chemical name is dihydrogen monoxide.

Question 2. c) \(\text{PbS}\)
Answer: Lead(II) sulphide (Galena)
In simple words: A natural mineral compound of lead and sulphur.

Exam Tip: Lead is denoted by Pb and sulphur by S.

Question 2. d) \(\text{CuO}\)
Answer: Copper(II) oxide (Cupric oxide)
In simple words: A black metal oxide of copper.

Exam Tip: Cu has a valency of +2 and oxygen -2.

Question 3. Identify the elements in the following compounds and also how many atoms of each element are present in the following:
a) \(\text{Na}_2\text{CO}_3\)
Answer: Sodium (Na): 2 atoms
Carbon (C): 1 atom
Oxygen (O): 3 atoms
In simple words: Sodium carbonate contains three different elements with a total of 6 atoms.

Exam Tip: Multiply the subscript number by any preceding multiplier if applicable.

Question 3. b) \(\text{CaBr}_2\)
Answer: Calcium (Ca): 1 atom
Bromine (Br): 2 atoms
In simple words: Calcium bromide consists of one calcium and two bromine atoms.

Exam Tip: Subscripts indicate the exact number of atoms of each element in a single molecule.

Question 3. c) \(\text{Al}_2(\text{SO}_4)_3\)
Answer: Aluminium (Al): 2 atoms
Sulphur (S): 3 atoms
Oxygen (O): 12 atoms
In simple words: The subscript outside the bracket multiplies everything inside the bracket (1 sulphur \(\times\) 3 = 3, 4 oxygen \(\times\) 3 = 12).

Exam Tip: Always distribute numbers outside parentheses to all elements inside the parentheses.

Question 3. d) \(\text{C}_6\text{H}_{12}\text{O}_6\)
Answer: Carbon (C): 6 atoms
Hydrogen (H): 12 atoms
Oxygen (O): 6 atoms
In simple words: Glucose contains six carbon, twelve hydrogen, and six oxygen atoms.

Exam Tip: This is the standard molecular formula for glucose.

Question 4. Complete the table showing the arrangement of electrons and protons in hydrogen and chlorine for the compound \(\text{HCl}\).
Answer:

In simple words: Shell capacity follows the \(2n^2\) rule: 2 electrons in the first shell, 8 in the second, and the remaining 7 in the third shell for chlorine.

Exam Tip: Atomic number equals the number of protons and electrons in a neutral atom.

BIOLOGY

Question I. Answer the following in one word.
a) These tissue forms the lining of various organs all over the body.
Answer: Epithelial tissue
In simple words: It acts as a protective covering for body surfaces and organs.

Exam Tip: Epithelial tissue covers both external surfaces and internal cavities.

Question I. b) These tissues are long and cylindrical in shape.
Answer: Muscle tissue (or striated muscle tissue)
In simple words: Muscle cells are elongated for contraction and movement.

Exam Tip: Skeletal muscle fibres are specifically long and cylindrical with multiple nuclei.

Question I. c) This cell conducts messages form one part of the body to the other.
Answer: Nerve cell (Neuron)
In simple words: Neurons transmit electrical impulses throughout the nervous system.

Exam Tip: Neurons are the longest cells in the human body.

Question I. d) This a blood like fluid lacking the red blood cells.
Answer: Lymph
In simple words: Lymph is plasma-like fluid without red blood cells that helps in immunity.

Exam Tip: Lymph flows through the lymphatic system and contains white blood cells.

Question I. e) This connectiv e tissue is found in the nose and in the external ear.
Answer: Cartilage
In simple words: Cartilage is a flexible and supportive connective tissue.

Exam Tip: Unlike bone, cartilage has a semi-rigid matrix that provides flexibility.

Question II. Draw the different types of muscular tissues and write down its function.
Answer: There are three main types of muscular tissues:
1. Skeletal Muscle: Cylindrical, unbranched, and striated with multiple nuclei. Function: Responsible for voluntary body movements and locomotion.
2. Smooth Muscle: Spindle-shaped and non-striated with a single central nucleus. Function: Controls involuntary movements in internal organs like the stomach, intestine, and blood vessels.
3. Cardiac Muscle: Cylindrical, branched, and striated with intercalated discs. Function: Responsible for the rhythmic, involuntary contraction and relaxation of the heart.
In simple words: Muscles help the body move, pump blood, and control internal organ functions.

Exam Tip: Learn to distinguish between voluntary (skeletal) and involuntary (smooth and cardiac) muscles based on their structure and location.